Mannosidosis of Angus cattle is being studied as a model lysosomal storage disease and with particular reference to principles of heterozygote detection and understanding the principles of enzyme replacement therapy. Other storage diseases which are being developed as similar models of analogous human disease include canine Gaucher's disease and ovine ceroid-lipofuscinosis. The pathogenesis of this latter group of human diseases is unknown and emphasis is to be placed on this aspect in this model. Heterozygous herds, flocked and colonies of heterozygous individuals have been or are being established for each model. As our research is becoming more broad based we see collaborative studies as being of particular importance and collaboration on some aspects has been arranged. The objective has been, and remains, to define each model in depth in regard to pathology, pathogenesis, dynamics of storage and excretion of storage material and characteristics of the mutant enzyme as a basis to a logical stepwise approach to development of specific or non-specific therapeutic strategies. In regard to these, some experiments may be designed on an organ rather than whole animal approach so that specific questions can be answered. Other models, if they are found, may be likewise developed and similarly made available to other research workers.